Front-ends: Remove now defunct afterEOF and related, use scanner's instead.

Code using atEndOfFile was dead, instead do something useful with
the scanners atEndOfInput().  This allows a better error message
for early termination of cascading errors.

glslang/MachineIndependent/Scan.h

@@ -204,6 +204,8 @@ public:
         currentSource = numSources;
     }
 
+    bool atEndOfInput() const { return endOfFileReached; }
+
     const TSourceLoc& getSourceLoc() const
     {
         if (singleLogical) {